The present disclosure generally relates to wellbore servicing fluids. More particularly, this disclosure relates to microemulsifiers and methods of making and using same.
Natural resources such as gas, oil, and water residing in a subterranean formation or zone are usually recovered by drilling a wellbore down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run in the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus, which is located between the exterior of the casing and the walls of the wellbore.
During drilling and as the drilling fluid is circulated upward through the annulus, a thin layer of residue is deposited on the annulus between the exterior of the drill string and/or the casing and the walls of the wellbore. The thin layer of residue is referred to as a filtercake and aids in controlling drilling fluid from leaking-off into the subterranean formation. After drilling and casing the wellbore, the well has to be emptied of drilling mud before it can be completed. Additionally, prior to production, the casing may be cleaned (e.g., removal of oleaginous fluid contaminants) and/or the filtercake removed. Cleaning of the casing may improve adherence of the casing to the cement composition used to seal the annulus and removal of the filtercake may be advantageous as its presence would restrict the inflow of hydrocarbons into the wellbore. The completion fluid used to displace the drilling mud is typically a brine composed of water and a suitable salt (e.g., sodium chloride, zinc bromide, calcium chloride) and may contain additional components that facilitate the cleaning of the casing and/or the removal of the filtercake. Such additional components should promote the efficient cleaning of the casing and/or removal of the filtercake while in contact with the high salinity solution (e.g., brine). For example, the completion fluid may contain one or more surfactants such as cationic, anionic, and non-ionic surfactants. A non-ionic surfactant may be considered for use in high salinity solutions (e.g., brines) due to their increased salt tolerance and indifference to multivalent ions. However, drawbacks to the use of non-ionic surfactants in a completion fluid include the presence of an upper temperature limit for stability of microemulsions comprising the non-ionic surfactants. Without wishing to be limited by theory, this thermal instability may be attributable to dehydration of ethoxylate groups of the non-ionic surfactant as the temperature is increased. This phenomenon is referred to as the cloud point and it is where the non-ionic surfactant has a drastic reduction in its solubility causing it to phase separate. Additionally, a specific non-ionic surfactant may have to be chosen for a removal of a specific oleaginous fluid and as such may display a reduced versatility when compared to other types of surfactants.
A cationic or anionic surfactant while displaying increased stability and versatility when compared to a non-ionic surfactant may also have drawbacks associated with its use. For example, anionic surfactants may exhibit reduced effectiveness in brines composed of multivalent ions (e.g. Ca2+ or Zn2+) while cationic surfactants which are compatible with most completion brines typically have toxicity issues associated with their use. Thus, it would be desirable to develop compositions and methods for cleaning a casing and/or removing a filtercake from a subterranean formation that are compatible with brines.